An endotracheal tube (ETT) is commonly used in medical procedures, such as during anesthesia, intensive care, and emergency care, to provide an open airway to the patient's lungs, as may be required, for example, for mechanical ventilation. The ETT is inserted into the patient's trachea, in a process known as intubation, and typically a balloon-like cuff near the distal end of the tube is inflated to secure the tube within the trachea and prevent leaks around the tube.
When intubating a patient, it is important to avoid over-inflation of the cuff, since excessive cuff pressure against the tracheal wall can cause mucosal ischemia, and the subsequent pressure necrosis can lead to tracheal stenosis. Other catastrophic complications of an over-inflated cuff include mucosal ulceration, perforation, scarring and rupture of the trachea, and fistula.
It is also critical that the cuff is sufficiently inflated to adequately seal against the tracheal wall. Consequences of an under-inflated cuff include not only air leakage around the tube, but also serious complications such as silent aspiration of secretions and other foreign material, which can lead to pneumonia and other serious conditions.
Therefore, in order to avoid these myriad problems relating to both over-inflation and under-inflation of an ETT cuff, it is imperative that the cuff is inflated to a pressure that falls within a narrow range of acceptable cuff pressures. Furthermore, unsafe cuff pressures can develop in an intubated patient over time. Leaks in the cuff or elsewhere in the ETT can result in a gradual pressure loss, and absorption by the cuff of certain gases, such as nitrous oxide, can actually increase cuff pressure during intubation. Changes in patient conditions over prolonged period may also require adjustments to the cuff pressure. Therefore, it is important that the cuff pressure is routinely monitored and maintained within the acceptable pressure range.
Differences in anatomy and opposing tracheal pressures amongst individuals render the volume of the fluid within the cuff an inaccurate proxy for cuff pressure, even in identically-sized cuffs. Thus, the cuff pressure cannot be reliably controlled by simply maintaining a pre-determined volume of air within the cuff.
Presently, the most common technique used by clinicians for monitoring cuff pressure is to estimate the pressure by finger palpation of the syringe used to inflate the cuff, or in some cases, finger palpation of a pilot balloon external to the patient and in fluid communication with the cuff. This technique has been demonstrated to be highly inaccurate. Syringe employed to inflate the cuff have been adopted to measure pressure but have failed to provide the sensitivity and range for reliable cuff pressure measurement. Another approach is to directly measure the cuff pressure by attaching a separate manometer to the inlet valve of the cuff. However, manometers are bulky, expensive devices that are typically not used nor readily available at the point-of-care. Furthermore, these devices are not always accurate, since many pressure gauges add compressible volume which can affect measurement and can even negatively effect cuff pressure as a result of the measurement.